Wurtzitic and cubic boron nitrides are extremely hard refractory materials which possess superior properties as compared to diamond when used for grinding or cutting of materials containing nickel, cobalt or iron. These metals, i.e., nickel, cobalt and iron, and their alloys, are known to chemically attack diamond at the hot cutting edge. Thus, cutting tools with diamond cutting edges, deteriorate quickly when used to cut these metals or their alloys and are, therefore, expensive to use.
Though expensive, diamonds are used for cutting tools because boron nitrides, such as cubic born nitride, or wurtzitic boron nitride, are even more expensive overall.
Wurtzitic and cubic boron nitrides are expensive because they are not naturally occurring, and the process used to make them involves the use of expensive high temperature-high pressure equipment and reactants that are relatively expensive.
Boron nitride can be found in at least five different states, i.e., hexagonal boron nitride, rhombohedral boron nitride, graphitic boron nitride, wurtzitic boron nitride, and cubic boron nitride. Of the five states, cubic boron nitride is most desirable because it is the hardest. It is suitable for use not only as a cutting tool, but also as a crucible in the melting of metals, as a polishing material and the like.